1. Field of the Invention
The present invention relates to a perpendicular magnetic recording medium used as magnetic tape or a magnetic disk, and a process for manufacturing it.
2. Description of the Prior Art
A magnetic disk is demanded for higher and higher surface recording density because a hard disk has higher and higher capacity and a smaller and smaller size accompanying with recent advancement of a personal computer or workstation. However, the longitudinal recording method which is widely used at present suffers from problems of thermal fluctuation from recording magnetization due to miniaturization of recording bit, and increase of coercive force which may exceed the recording capability of the recording head when it is intended to attain high-recording density. Thus, the perpendicular magnetic recording method is being studied as an approach which can significantly increase the surface recording density. It is a so-called double-layer perpendicular medium consisting of a soft magnetic underlayer film with high permeability and a perpendicular magnetizing film with high perpendicular anisotropy that is considered promising as a perpendicular magnetic recording medium to attain the above.
FIG. 1 is a schematic sectional view showing such a conventional perpendicular magnetic recording medium.
This perpendicular magnetic recording medium 50 is formed by laminating a soft magnetic underlayer film 56 and a perpendicular magnetizing film 58 on a substrate 52 in this order. For example, an NiFe film is used as the soft magnetic underlayer film 56, and a CoCr type alloy film is used as the perpendicular magnetizing film 58. However, crystalline orientation of the perpendicular magnetizing film 58 is degraded when the soft magnetic underlayer film 56 of NiFe and the perpendicular magnetizing film 58 of CoCr are formed. Then, to prevent this, it is reported to use a Sendust film (FeSiAl alloy) as the soft magnetic underlayer film 56 (Japanese Patent Application Laid-Open No. 57-36435)
However, such conventional perpendicular magnetic recording medium has limitation in lowering media noise and improving recording density dependence on read output voltage.
Then, the object of the present invention is to provide a perpendicular magnetic recording medium which can further lower the media noise, and further improve the recording density dependence of read output voltage and manufacturing process therefor.
The inventors have reached the following view on the reasons preventing lowering of media noise and improvement of recording density dependence of read output voltage through repeated experiments and observations. That is, poor surface smoothness of the soft magnetic underlayer film degrades the perpendicular orientation of the perpendicular magnetizing film formed thereon. Therefore, as thickness of an initial layer (region in which crystal is not perpendicularly oriented) increases, surface smoothness of the perpendicular magnetizing film is degraded, so that the media noise is not lowered. In addition, since the perpendicular orientation is degraded for the perpendicular magnetizing film, the recording density dependence of read output voltage cannot be improved. The present invention is made based on such view.
A first aspect of the present invention is a perpendicular magnetic recording media and its manufacturing process, wherein a perpendicular magnetic recording medium comprises a soft magnetic underlayer film and a perpendicular magnetizing film, these films being formed on a substrate in this order, a Cr film being inserted between the substrate and the soft magnetic underlayer film. The Cr film has very excellent surface smoothness. Therefore, the soft magnetic underlayer film laminated on the Cr film also has very excellent surface smoothness reflecting the surface smoothness of the Cr film. Therefore, perpendicular orientation and surface smoothness are improved for the perpendicular magnetizing film laminated on the smooth surface of the soft magnetic underlayer film. As the perpendicular orientation is improved for the perpendicular magnetizing film, the initial layer is reduced, thereby media noise being lowered and recording density dependence of read output voltage being improved. In addition, as the surface smoothness is improved for the perpendicular magnetizing film, sliding characteristics of a recording/reproducing head is also improved, thereby this also lowering the media noise.
In the perpendicular magnetic recording medium and its manufacturing process according to the first aspect of the present invention, the soft magnetic underlayer film is, for example, an FeSiAl film, and the perpendicular magnetizing film is a CoCrTa film. In addition, average surface roughness on the centerline on the soft magnetic underlayer film is preferably 2 nm or less, more preferably 0.9 nm or less, most preferably 0.5 nm or less. Such surface smoothness can be obtained by sputtering under gas pressure of less than preferably 20 mTorr, more preferably 4 mTorr or less. Gas used in this case is Argon, for example. In addition, film thickness of the perpendicular magnetizing film is preferably more than 20 nm but 150 nm or less, more preferably 50 nm or more but 150 nm or less. The media noise is further reduced in these ranges. Furthermore, a Ti film or non-magnetic CoCr film may be inserted between the soft magnetic underlayer film and the perpendicular magnetizing film. In this case, the perpendicular orientation is further improved for the perpendicular magnetizing film.
A second aspect of the present invention is a perpendicular magnetic recording media and its manufacturing process, wherein a perpendicular magnetic recording medium comprises a soft magnetic underlayer film and a perpendicular magnetizing film, these films being formed on a substrate in this order, a smoothness control film being inserted between the substrate and the soft magnetic underlayer film. A material of the smoothness control film is one of nine types of (1) C, (2) Ti, (3) alloy containing Cr, (4) alloy containing Ti, (5) alloy containing C, (6) alloy containing Cr and Ti, (7) alloy containing Ti and C, (8) alloy containing C and Cr, and (9) alloy containing Cr, Ti and C. The smoothness control film of such material has very excellent surface smoothness. Therefore, the soft magnetic underlayer film laminated on the smoothness control film also has very excellent surface smoothness reflecting the surface smoothness of the smoothness control film. Therefore, perpendicular orientation and surface smoothness are improved for the perpendicular magnetizing film laminated on the smooth surface of the soft magnetic underlayer film. As the perpendicular orientation is improved for the perpendicular magnetizing film, the initial layer is reduced, thereby media noise being lowered and recording density dependence of read output voltage being improved. In addition, as the surface smoothness is improved for the perpendicular magnetizing film, sliding characteristics of a recording/reproducing head is also improved, thereby this also lowering the media noise.
In the perpendicular magnetic recording medium and its manufacturing process according to the second aspect of the present invention, the soft magnetic underlayer film is, for example, an FeSiAl film or an FeTaN film. The perpendicular magnetizing film is, for example, a CoCrTa film. In addition, average surface roughness on the centerline on the soft magnetic underlayer film is preferably 2 nm or less, more preferably 0.9 nm or less, most preferably 0.5 nm or less. Film thickness of the smoothness control film is preferably more than 1 nm but less than 17 nm, more preferably 2 nm or more but 15 nm or less. Gas pressure in sputtering film formation of the smoothness control film is preferably less than 20 mTorr, more preferably 18 mTorr or less. Film formation speed in sputtering film formation of the smoothness control film is preferably less than 20 nm/s, more preferably 18 nm/s or less. Gas used for the sputtering film formation is, for example, Argon, Krypton, Neon and the like.
A third aspect of the present invention is a perpendicular magnetic recording media and its manufacturing process, wherein a perpendicular magnetic recording medium comprises a soft magnetic underlayer film and a perpendicular magnetizing film, these films being formed on a substrate in this order, a Cr film with a specific film thickness being inserted between the substrate and the soft magnetic underlayer film. Film thickness of the Cr film is 1 nm or more but less than 17 nm, preferably 2 nm or more but 15 nm or less. The Cr film with such film thickness has very excellent surface smoothness. Therefore, the soft magnetic underlayer film laminated on the Cr film also has very excellent surface smoothness reflecting the surface smoothness of the smoothness control film. Therefore, perpendicular orientation and surface smoothness are improved for the perpendicular magnetizing film laminated on the smooth surface of the soft magnetic underlayer film. As the perpendicular orientation is improved for the perpendicular magnetizing film, the initial layer is reduced, thereby media noise being lowered and recording density dependence of read output voltage being improved. In addition, as the surface smoothness is improved for the perpendicular magnetizing film, sliding characteristics of a recording/reproducing head is also improved, thereby this also lowering the media noise.
In the perpendicular magnetic recording medium and its manufacturing process according to the third aspect of the present invention, the soft magnetic underlayer film is, for example, an FeSiAl film or an FeTaN film. The perpendicular magnetizing film is, for example, a CoCrTa film. In addition, average surface roughness on the centerline on the soft magnetic underlayer film is preferably 2 nm or less, more preferably 0.9 nm or less, most preferably 0.5 nm or less. Gas pressure in sputtering film formation of the Cr film is preferably less than 20 mTorr, more preferably 18 mTorr or less. Film formation speed in sputtering film formation of the Cr film is preferably less than 20 nm/s, more preferably 18 nm/s or less. Gas used for the sputtering film formation is, for example, Argon, Krypton, Neon and the like.